A microwave filter is a type of lossless two-port network that is widely applied to microwave communication, radar, electronic countermeasure, and a microwave measurement instrument. The microwave filter is used to control a frequency response of a signal in a system, so that frequency component of a wanted signal passes through the filter almost without attenuation, and transmission of frequency component of an unwanted signal is blocked.
With development of modern microwave communication, in particular, satellite communication and mobile communication, the system has a higher selection of a path. As the microwave filter is an important part in a communications system, performance of the microwave filter determines quality of the whole communications system.
As shown in FIG. 1, an existing microwave filter generally includes a rectangular waveguide 31 and a diaphragm 12 that is metallic at least on the surface and is vertically disposed in the rectangular waveguide 31, where the diaphragm 12 is located between an input port 31a and an output port 31b of the rectangular waveguide 31 and has at least one window 15, and the window 15 of the diaphragm 12 and a surrounding cavity of the window 15 form a series of resonant units. The input port of the rectangular waveguide refers to a port through which a signal is inputted to the rectangular waveguide, and the output port refers to a port through which a signal is outputted from the rectangular waveguide (for example, if the rectangular waveguide is a rectangular waveguide in a microwave filter, the signal is a microwave signal). The microwave filter is generally corresponding to only a fixed operating band. If an operating band required by an existing network changes and does not suit the fixed operating band of the microwave filter, the system can work normally only by replacing with a suitable device, and therefore, device costs are relatively high.